two concentric circles are drawn so that the shaded area is equal to unshaded area. The radius of the outer circle is 6 cm. Find the difference in the radii of the two circles

\(\pi r^2 = \pi R^2 - \pi r^2\\ 2\pi r^2 = 36\pi\\ r^2 = 18\\ r=3\sqrt2\\ R-r = 6-3\sqrt2\)